Circuit boards are capable of connecting with other circuit boards through connecting devices such as circuit board connectors, cables, backplanes, and the like. One conventional circuit board assembly includes a relatively large primary circuit board, and a smaller circuit board. The larger primary circuit board includes circuitry (e.g., a combination of integrated circuit devices, resistors, capacitors, etc.) that performs primary operations of the circuit board assembly, i.e., data storage operations. The smaller circuit board performs a specialized function, i.e., power conversion to supply the circuitry of the primary circuit board with a converted power signal.
To form this conventional circuit board assembly, the manufacturer lays the large primary circuit board horizontally and then inserts the ends of four power pins, one at a time, into large plated-through holes of the primary circuit board. The power pins are relatively thick, and have flanges which hold solder pre-forms in place near the ends of the power pins. After the manufacturer individually inserts the power pins into the primary circuit board, the manufacturer then holds the smaller circuit board in a horizontal position over the primary circuit board, and inserts the opposite ends of the power pins, one at a time, into large plated-through holes of the smaller circuit board to form an unsoldered circuit board assembly. The manufacturer then sends the unsoldered circuit board assembly through a soldering process. During this process, the solder pre-forms melt and flow around grooves at the ends of the power pins and into the plated-through holes to form solder joints. The grooves facilitate gas percolation out of the holes and enable the circuit boards and pins to fall accurately in place due to drawing action of the melted solder from the solder pre-forms. Circuit board components which were previously mounted on the circuit boards (e.g., to the circuit board undersides) do not significantly re-flow during the soldering process because they were previously mounted using high temperature solder, i.e., their solder joints have a higher melting temperature than that used during the soldering process.
The end result of the assembly process is a circuit board assembly having a large circuit board and a small circuit board which are parallel to each other. The power pins extend perpendicularly from the planes of the two circuit boards to provide electrical paths for carrying power signals therebetween, as well as to provide structural separation between the two circuit boards.
Unfortunately, there are deficiencies to the above-described conventional circuit board assembly which includes a large circuit board, a small circuit board and a four power pins soldered therebetween. For example, it takes time to meticulously align the power pins one at a time between the two circuit boards prior to soldering. Although the manufacturer could make the circuit board holes larger, and thus make it easier to fit the pin ends into the holes, the manufacturer may simultaneously create other drawbacks by doing so such as displacing neighboring traces and/or degrading signal integrity. If one of the power pins is misaligned, that pin will solder improperly between the two circuit boards, and thus not properly carry a power signal between the two circuit boards when the circuit board assembly is powered up. Accordingly, improper power pin alignment will cause the circuit board assembly to operate incorrectly or not operate at all.
Additionally, although it is possible to rework circuit board assemblies having improperly aligned and soldered power pins (e.g., the manufacturer can unsolder the two circuit boards and the power pins, clean the circuit boards, and re-solder the circuit boards together using new power pins), such reworking is an expensive and time consuming task. Moreover, there is always a risk that one or both of the circuit boards will be damaged beyond repair during the rework process forcing the manufacturer to scrap work product that was otherwise good in all other respects.
Furthermore, the earlier-described assembly steps for creating the conventional circuit board assembly is suitable when interconnecting two circuit boards using only four power pins but not well-suited for interconnecting two circuit boards with significantly more pins. For example, suppose that the manufacturer wants additional electrical pathways (e.g., more than 10 additional pathways) between to two circuit boards in order to carry control and status signals. Unfortunately, it is difficult for the manufacturer to interconnect the two circuit boards with other pins in addition to the four thick power pins (e.g., thinner signal pins for carrying data signals). In particular, as the number of pins increases, it becomes exceedingly more difficult for the manufacturer to properly position each pin one at a time into the primary circuit board and then to maintain proper pin registration as additional pins are added. Additionally, it becomes exceedingly more difficult for the manufacturer to subsequently place the smaller circuit board into engagement with all of the pins, as the number of pins increases. That is, for each additional pin, the installation time and the possibility of mis-registration of a pin increases. The increased installation time and the time required to rework improperly manufactured circuit board assemblies may thus significantly increase manufacturing expense.
Moreover, thinner signal pins typically solder to circuit boards using a wave soldering process, i.e., a soldering process which involves wicking up solder into a hole having a diameter that in some situations is roughly twice the signal pin diameter. The use of such holes and their associated large anti-pads (e.g., another 30 percent larger than the hole) can impose significant limitations to neighboring trace locations and can also create signal integrity problems. Of course, narrowing the holes makes it more difficult to wick up solder and to form reliable solder joints as well as makes it more difficult for the manufacturer to install the pins and the second circuit board. Accordingly, a manufacturer may be reluctant to add signal pins between two parallel circuit boards for enhanced connectivity (e.g., for carrying control signals therebetween).
One alternative to adding more pins between to the two circuit boards is for the manufacturer to add a circuit board connector to each circuit board. Unfortunately, the use of circuit board connectors requires additional circuit board real estate (i.e., surface area on the circuit boards in order to mount the connectors) which, in many instances, is very expensive. Moreover, the use of such connectors would provide competing stresses to the circuit boards during the soldering process which could result in damaged solder joints (e.g., mis-registration of the power pins prior to soldering, solder joint fractures after soldering, etc.).
In contrast to the above-described conventional circuit board assembly which is formed by a manufacturer (i) inserting ends of power pins into a first circuit board one at a time, (ii) inserting opposite ends of the power pins into a second circuit board, and (iii) soldering the power pins to the first and second circuit boards, the invention is directed to techniques for making circuit board assemblies which utilize a pin assembly having a set of pins and a frame which holds the set of pins in place. The pin assembly enables a manufacturer to simultaneously register ends of all of the pins into a first circuit board and then simultaneously register opposite ends of the all of the pins into a second circuit board. The frame holds the pins in place to ensure proper and consistent pin registration in each circuit board.
One embodiment of the invention is directed to a pin assembly for interconnecting a first circuit board and a second circuit board. The pin assembly includes a set of pins. Each pin of the set of pins has a first end, a second end, and a mid-portion. The pin assembly further includes a frame which contacts the mid-portion of each pin of the set of pins to position the pins such that (i) the first ends of the pins simultaneously register into respective holes of the first circuit board when the pin assembly engages with the first circuit board, and (ii) the second ends of the pins simultaneously register into respective holes of the second circuit board when the pin assembly engages with the second circuit board. The use of the pin assembly enables a circuit board assembly manufacturer to save time registering the pins while making circuit board assemblies. Additionally, use of the pin assembly enables the manufacturer to use an intrusive reflow process when soldering the pins (e.g., signal pins, power pins, or both) to the circuit boards due to the reliable pin positioning provided by the pin assembly thus enabling the circuit boards to have smaller anti-pads and thus freeing up circuit board real estate to alleviate trace congestion particularly around the circuit board holes. Furthermore, use of the pin assembly reduces or eliminates the possibility of having to rework the circuit board assembly due to improperly registered pins.
In one arrangement, each pin of the set of pins includes (i) outer flanges which are configured to seat that pin relative to the first and second circuit boards, and (ii) inner flanges which define the mid-portion of that pin and which are configured to hold the pin rigidly in place relative to the frame. Accordingly, such pin features facilitate positioning of the pins relative the frame, as well as facilitate positioning of the pins (and the pin assembly as a whole) relative to the circuit boards thus providing uniform pin insertion height.
In one arrangement, the frame includes a set of stress relief portions which is configured to flex in response to uneven stresses placed on the pin assembly. In one arrangement, the set of stress relief portions includes frame segments which define V-shaped notches. The stress relief portions reduce the likelihood of irregular bowing or buckling of the pin assembly due to uneven stresses during soldering. Accordingly, the pins remain well-positioned when heat is applied to solder the pin assembly to the circuit boards, i.e., the pins will not bind due to movement resulting from (i) different coefficients of expansion among circuit board materials during soldering, or (ii) the circuit boards warping toward or away from each other during soldering.
In one arrangement, the set of pins includes a set of power pins, and a set of signal pins. Each power pin of the set of power pins has a power pin diameter, and wherein each signal pin of the set of signal pins has a signal pin diameter that is narrower than the power pin diameter. Accordingly, the pin assembly is capable of carrying both power signals as well as data signals between the circuit boards thus alleviating the need for additional circuit board components such as additional circuit board connectors which require a significant additional amount of circuit board real estate.
In one arrangement, the frame defines a rectangular, skeletal shape. That is, the frame substantially extends around a periphery of the defined rectangular, skeletal shape while substantially avoiding an inner region of the defined rectangular, skeletal shape. Accordingly, the frame does not interfere (e.g., contact) with circuit board components which are mounted to the circuit boards and which extend outwardly near the frame.
The features of the invention, as described above, may be employed in systems, devices and procedures such as those of EMC Corporation of Hopkinton, Mass.